The passage suggests which of the following about bacteria studied microscopically?

A. They are likely to be misidentified several times before scientists reach a consensus.B. They cannot be developed in such a way to infect a laboratory animal.C. They are difficult to identify unless highlighted by conventional staining techniques.D. They are less likely to be the cause of a disease than bacteria grown on standard laboratory media.E. They are more challenging to analyze when placed on glass slides than on slides made of other materials.

(C) The specific bacteria discussed in the passage that is studied microscopically is the Legionella bacterium. Scientists failed to identify it for some time because conventional staining techniques did not 'take up' the bacteria, making it difficult to identify against the backdrop of a glass slide. Choice (C) is correct, as suggested by the relevant sentence in the first paragraph. While the causes of Legionnaire's were misidentified several times, we don't know whether that's generally true, eliminating (A). (B) confuses the microscopic theory with the first theory presented at the beginning of the passage, which is the same as the problem with (D). (E) focuses too much on the glass slides; the difficulty in identifying Legionella had more to do with the staining process than any details in the makeup of the slides.

The first sentence of the last paragraph of the passage ("However, pinning down the precise cause of a new disease is always full of pitfalls and wrong turns..") tempts me to pick A. This sentence generalizes but the reasoning given for why ' A' is wrong is that we don't know whether misidentification is generally true.

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